The overall objective of this proposal is to elucidate the pathways of glutamine metabolism in neonates and to determine how prematurity and surgical stress alter these pathways. Glutamine, an important fuel for lymphocytes and intestinal epithelial cells, may be an indispensable amino acid in premature and surgically stressed infants. Consequently, determining the capacity of these infants to synthesize glutamine and the regulation of the release of glutamine from existing body protein is important. Glutamine supplementation may play a critical role in supporting optimal protein accretion, recovery from intestinal injury, and immune function in these particularly vulnerable infants. The specific aims of this proposal are to determine how rates of de novo glutamine synthesis and release of glutamine from body protein are altered by prematurity and surgical stress in: 1) the basal state 2) in response to the provision of parenteral nutrition and 3) in response to the provision of parenteral nutrition with supplemental glutamine. These specific aims will be pursued using stable isotope tracers. Performing these studies will provide insight into the metabolism of glutamine and ultimately, may serve as the basis for improved nutritional management of premature and surgically stressed infants.